Treatment of whiting and the like



Patented ar. :24, 1936 TREATMENT OF WRITING AND THE LIKE John W. Church and Raymond B. McClure, Painesville, Ohio, assignors to Pure Calcium Products Company, Pai

ration of Ohio nesville, Ohio, a corpo- No Drawing. Application August 22, 1933, Serial No. 686,240. In Canada November 21, 1931 21 Claims. (01. 134-58) The present invention relates to the treatment. of whiting and the like to improve its properties for use as a filler for plastics such as paints, enamels, rubber compositions, putty, etc.

This application is a continuation in part of our copending applications Serial No. 640,527, filed October 31, 1932,Serial No. 625,530, filed July 28, 1932, and Serial No. 578,614, filed December 2, 1931. Serial No. 640,527 was a continuation in part of our applications Serial Nos. 578,614 and 625,530. Serial No. 578,614 was a continuation in part of our application Serial No. 481,908, filed September 15, 1930. Serial No. 625,530 was a continuation in part of our application Serial No. 492,354, filed October 30, 1930.

The object of our invention is to produce from relatively inexpensive substances, such as whiting or the like, materials which will fill, to a large extent, the pasition now held by other more expensive materials in the paint, rubber and plastic industries.

The requirements for pigments in general (including fillers) are twofold in these industries; (1) their coloring or covering eifect, and (2) their effect on the life and strength of the compositions in which they are used.

We are concerned primarily with the latter function. As an instance of this second function, we may say that, for instance, carbon black is used in rubber as a reinforcing pigment. Its black color is really of little value, but the physical properties, such as the increased resistance to wear and tear which it imparts to such rubber goods as tire tread stocks, are vital. White lead (basic lead carbonate) is used in exterior house paint not entirely because it is a white covering pigment (because it has relatively low hiding power), but because it imparts to the paint film the characteristic of resisting the elements better than other pigments. As an instance, pure titanium dioxide has much higher hiding power than white lead, but it cannot be used effectively alone in exterior paints because it induces early and severe chalking.

Carbon black is vital to the rubber industry because it is capable of forming a true bond with the rubber matrix. This bondability is believed to be due' to the intimate presence on each particle of carbon black of a sufiicient amount of organic material which is capable of forming a strong bond between the carbon black particle and the rubber.

White lead bonds with the linseed oil vehicle commonly used in exterior paints by means of its reaction with the acidic substances in the oil, so that a film of lead soap is formed on the exterior of the white lead particle. The soap having its interior bond in the white lead itself and its exterior bond being organic and capable of bonding strongly with the oil matrix, forms a very cohesive paint film which endures for long periods of time against the elements. Zinc oxide forms a similar bond with vehicles due to soap formation. Zinc soaps, however, are extremely hard and brittle and allow little or no elasticity in the 5 paint film, so that zinc oxide alone is not fully desirable for use in exterior house paints inas much as it will induce cracking, which is the opposite of chalking. Zinc oxide, however, is often used in exterior paints in combination with nonwetting or non-bonding pigments and fillers which are prone to chalk, as a counterbalance against chalking. Zinc oxide is also reinforcing in rubber probably because it forms soaps with the rubber acids.

The so-called fillers, such as whiting, barytes, magnesium silicate, etc., are notoriously poor bonding materials and they are used to a very limited extent in exterior and interior paints of good quality. Likewise, they make poor bonds with rubber and cannot be used in large quantity except in rubber goods of comparatively inferior quality. This lack of bondability may be explained by the lack of any bonding agent on the surface of such particles and their non-reacting g to form such bonds with the acids present in the matrix.

If fillers could be obtained which were truly bendable with matrices such as oil and varnish,

and rubber, their use would be much extended inexpensive materials as whiting and the like may and severe attrition. preferably in a ball mill, I

together with a small amount of a material, such as stearic acid or rosin, which will serve the dual function 'of an anti-compactant and an interbonding agent. These materials serve as anticompactants to permit the grinding to be prolonged far beyond that possible without the anticompactant action of such substances. They also serve as interbonding agents in causing a firm bond between the whiting particles and the matrix, such as rubber or paint oils, probably by forming thin surface films on the whiting particles.

A charge of dry powdered whiting. preferably precipitated whiting, is put into the ball mill,

together with a small quantity, say, about 1 to 3%,

of the anti-compactant and interbonding agent, such, for example, as rosin, which is principally abietic acid. The mill is then started and the first action is a general dissemination of the rosin throughout the body of the whiting. After a short time the material becomes decidedly free flowing, that is to say, it has many of the char-.

acteristics of a liquid in that it cannot be held on a lmife blade, it seeks its own level and will flow through very small openings. When the material is in such free flowing stage it can be acted upon very eflectively by the grinding balls since it will not cake upon the balls, and will allow the balls to come in contact with each other to exert a very severe shearing and attrition action upon the particles of the whiting caught between to displace the adsorbed gas films from the particles and replace them with very thin films of calcium resinate. When the rosin is pounded into intimate contact with the surfaces of the particles, it combines chemically with the calcium carbonate to form a very thin film of calcium resinate. The aggregate surface areas of the minute particles is enormous and it requires a very prolonged and severe attrition or grinding to thoroughly spread the rosin over and pound it into intimate contact with the surfaces of all of the whiting particles. v

After the initial grinding and after the resin becomes thoroughly disseminated through the whiting, an evolution of gas from the whiting is noted. The gas comes from the adsorbed gas films which are being displaced by the rosin, and also, to some extent, from the gas evolved by the chemical combination of the rosin with the calcium carbonate. The anticompactant action of the rosin is believed to be due primarily to its action in producing such gas which remains en-- trapped as free gas in the mass of the whiting,

serving as gaseous cushions between the whitingly all of the displaceable adsorbed gas films have.

been removed and replaced by the films of calcium resinate. If the grinding is continued long enough, the material finally passes from the free flowing state into a compacted state in which it cakes against the sides of the mill and between the balls, and prevents further effective grinding. Also, after the material has been compacted it ceases to be of value as a filler since it becomes non-dispersable in plastic matrices. When the material passes from the free flowing state to the compacted state there is a drop in the power required to drive the mill, showing that less work is then being done upon the whiting.

If the whiting were put into the ball mill and ground without the use of some agent, such as rosin or stearic acid, the whiting would remain in a loose grindable condition for but a relatively accordance with our process. Theactlon of the,

rosin or stearic acid isto prolong the loose 01 free flowing condition of the whiting for a period several times what it would have been if the rosin or stearic acid were not employed. The dual functions of the rosin or the stearic acid as an anti-compactant and as an interbonding agent, are probably manifestations or functions of a single phenomenon. They probably serve as anti-compactants because of their ability to become spread into tightly adherent and probably chemically combined very thin films on the surfaces of the particles, thereby displacing the adsorbed gas films and releasing such gas which in turn is entrapped in the mass of the whiting and serves to maintain the whiting in a loose free flowing condition as the grinding is continued. They also serve as eifective interbonding agents because during the prolonged. grinding made possible by their anti-compactant action, they are thoroughly disseminated over and pounded into the large surface areas of the powdered material so as to form films having sufiiciently intimate contact with the particles to displace substantially all of the adsorbed gas and having suflicient adhesion and strength to act as strong linkages or bonds between the particle and the matrix employed, such as the paint oil or the rubber.

Chemical analyses of the whiting ground with rosin shows that the rosin when ground according to our process is substantially all converted to calcium resinate, and similarly, when ground with stearic acid, the stearic acid is converted substantially all to calcium stearate. This indicates that the interbonding films are so thin as to be of molecular proportions, allowing substantially all of the rosin or stearlc acid molecules to react with the calcium carbonate surfaces. There is evidence that in very thin films of this character the molecules tend to orient themselves so that a molecule of calcium resinate is oriented with its calcium end against the whiting particle and its resinate end outwardly, and similarly in the case of a calcium stearate particle. Such films are therefore believed to have a strong inorganic bond with the whiting particle itself, and to form a strong organic bond with the matrix employed, thus completing the linkage. Whatever may be the reason, the bond has a strength and character similar to the reactive bonding of the reactive pigments, such as white lead and zinc oxide, or reinforcing pigments such as carbon black.

In order to impart to the whiting or similar substance the properties hereinafter more particularly described, which permit its successful substitution for the more expensive pigments of the type indicated above, a combination of certain factors appears to be involved:

1. The whiting is subjected to a very severe attrition prolonged far beyond the grinding processes heretofore employed in treating whiting and far beyond the grinding to which it would be possible to subject'the whit-ing if it were not for the anti-compactant action of the anti-compactant interbonding agent which we employ.

2. The agent which we employ serves as an effective antl-compactant so as to maintain the whiting in a free flowing condition for a considerable period of time, so that the grinding may be prolonged far beyond that possible without such anti-compactant action.

3. There is a rather narrow margin in the amount of the anti-compactant interbonding agent employed. It should be used in sumcient amount to serve as an interbonding agent in the Gil finished material, as well as to maintain the maover, the amount employed should not leave a I substantial excess over that which can be held combined with the whiting particle surfaces in the form of thin probably mono-molecular films.

For example, if too much rosin or stearic acid is employed, there will be free rosin or stearic acid which may have a deleterious effect upon the paint or rubber composition. In using agents, such as rosin and stearic acid, we find that they should be used in amounts from about .1% to 5% depending upon the particle size and effect desired, preferably from about 1% to 3%.

4. The agent added should, in addition to serving as an anti-compactant during grinding, serve as an interbonding agent in the treated whiting so as to firmly bond the whiting particles withthe bonding matrix employed in the plastic in question, such as a paint, rubber composition, putty, etc.

Our work with various fillers and interbonding agents indicates that they should be of the following character:

(a) The filler treated should be whiting or other alkaline earth metal carbonate, or a material containing such carbonate, since this class of materials apparently has some reaction with the interbonding agents employed, whereby the interbonding films have a linkage with the particles comparable with a molecularly attached bond. In the class of alkaline earth metals we include magnesium, as well as calcium, barium and strontium. Calcium carbonate is, however, preferred since this type of bond is more easily formed than with the other carbonates. Since materials containing such carbonates are susceptible to our process, as well as the pure carbonates, when we speak of alkaline earth metal carbonates in our claims, we intend to include not only the pure carbonates, but also materials containing such carbonates.

The various fillers and pigments appear to be classifiable in-three general classes according to their reactivity with the usual organic matrices or bonding media. One class includes such reactive substances as basic lead carbonate and zinc oxide, which are sufiiciently reactive to re-, act with linseed oil in the paint and form a soap which serves as an interbonding agent. Similar action apparently occurs when zinc oxide is added to rubber by a reaction between the zinc oxide and the acidic substances of the rubber. In this class might be included carbon black, which in its formation acquires a film of organic substance which is, on the one hand, strongly .bonded to the carbon particle, and on the other hand, strongly capable of bonding with a matrix such as rubber. Another class includes those filler materials, such, for example, as the sulphates and silicates, which are chemically so stable that they appear to be capable of substantialy no reaction with the usual organic matrices and bonding media. A third and intermediate class appears to be the alkaline earth metal carbonates, which are not reactive enough so as to secure reactive bonding with paint oils or with rubber by ordinary processes of mixing. These carbonates, however, appear to have enough reactivity to form a reactive type of bond with the interbonding agents which we employ when such interbonding agents are brought into such very intimate contact with the carbonate particles by the prolonged and severe grinding of our process. Calcium carbonate appears to be best adapted to our process since its surface molecules are relatively unstable and apparently contain some of their calcium oxide in equilibrium with adsorbed carbon dioxide gas. We believe that there is some chemical action which takes place between the unstable carbonate surface and the interbonding agent, when the in terbonding agent is intimately ground against the calcium carbonate surfaces in our process.

Whatever may be the chemical reason, the alkaline earth metal carbonates appear to be a class of substances which are capable of the reactive type of bonding under these conditions, and this is particularfy true of calcium carbonate; as distinguished, on the one hand, from substances in which reactive bonding can be accomplished without special precautions as in the case of basic lead carbonate and zinc oxide, and on the other hand, from those substances which as a class are not capable of reactive bonding, such as the sulphates and silicates.

(b) The interbonding agent should be a substance which forms, or is capable either in whole or in part of forming, a bond comparable to that of a molecular attachment with the surface of the material of the filler being ground. For example, resin and stearic acid react with calcium carbonate to form calcium resinate or calcium stearate. An agent, such as linseed oil, which contains some acidic substances, is capable of reacting in part with the carbonate particles. Agents, such as calcium resinate or calcium stearate, may be used, since they are already in the form of an organic soap or salt and the molecules can concurrentiy form the desired inorganic bond with the whiting and the organic bond with the plastic matrix. Certain gums, such as ester gum, have a similar action, probably due to some acidic bodies contained in them. Certain of the higher alcohols also bond in the desired manner, possibly because of their semiacidic nature. y

We will next specifically describe certain commercial procedures in treating artificial whiting inaccordance with our process.

The artificial whiting is first produced by precipitation by any of the well-known methods of producing precipitated whiting. The particle size can be controlled by the precipitating process, as is also well known. Precipitated whiting can be produced having very small particle sizes varying from micron average diameter to 5 microns average diameter. The whiting can be precipitated free from foreign substances, such as silica or other materials which are abrasive and which would give ball wear and also discolor the whiting because of abrading metal from the mill and its grinding elements during the pr longed grinding in our process. For producing a high grade material, particularly for use in paints, it is important that the materal be free from such discoloration.

In making a material which we have furnished to the paint industry, precipitated whiting of average particle size of about 5 microns and of a whiteness equal to that of pure magnesium carbonate is ground in a ba'l mill with about 1% water white rosin. The particular mill which we have employed is a ball mill 5 feet in diameter by 10 feet long which contains about 45% by volume of inch diameter hardened steel balls. The mill is equipped with lifter bars which are in the form of ribs extending about Y4 inch in from the inner surface of the cylinder. The mill is operated at a speed of approximately 83% of the critical speed.

This mill is charged with about 4,000 pounds of precipitated whiting, together with about 40 pounds of the water white rosin. The mill is driven until the whiting has practically passed through the free flowing stage, and the material is discharged just before it would begin to compact if the grinding were further continued. With the mill and charge described, the grinding period is about to '7 hours. A charge of this amount and particle size would, if ground without the anti-compactant, become so caked after about 2 hours grinding as to prevent any effective grinding thereafter.

In making a material which we have furnished to the rubber industry, the same mill is charged with about 3,600 pounds of precipitated whiting.

of a particle size averaging about V2 micron diameter together with about 36 pounds of stearicacid. The mill is operated with a cataracting action of the steel balls until thereis a drop in the power required to drive the mill, and then the material is discharged after about 1 /2 to 2 hours grinding. This point coincides with the transition of the material from the free flowing stage to the compacted stage and the material is preferably discharged while it still retains some of its free flowing characteristics. charge, because of its smaller particle size and lesser poundage would, if ground without the anti-compactant, be so caked atthe end of minutes grinding as to prevent the further eifective grinding.

We have also operated continuous mills. For example, we have ground precipitated whiting in accordance with our process in a continuous ball mill 6 feet in diameter and 22 feet long equipped with lifter bars and run at approximately 70% critical speed. The ball load is of 55 inch diameter hardened steel balls fllling about 40% of the volume of the mill. The mill is equipped with continuous feed and discharge apparatus. The rate of feed is such that the time of retention of the whiting in the mill is suflicient to subject it to the very prolonged and severe attrition characteristic of our process, which is made possible by the use of our anticompactant, and the whiting is discharged, preferably at or near the end of the free flowing period.

In each case the anti-compactant prolongs the eifective grinding several times (two or more times) beyond that possible if the same charge were to be ground without the use of the anticompactant.

The following tests show an illustrated example of the relationship between the amoimt of anti-compactant used and the times of grinding, and in this case also the tensile strength imparted to rubber compositions in which the various whitings were incorporated.

The same basic material, namely, precipitated whiting, was used in each case. The whiting, both unground and ground for various lengths of time, was incorporated in a number of rubber compositions which were molded, cured and tested ,for tensile strength.

The results are shown in the following table:

Table 1 Amount Grindingtimeinhours stearic acid 0 .25 .6 l 2 -3 4 5 6 'lensilestrcngthslbs. per sq. in.

2 None 3500 5 .5 a 3750 3050 4250 4400 44(1) 6 l.0% 3000 4200 4250 4425 4475 4000 7 1.5% 4GB 4150 4250 4400 4550 4750 8 2% 4M 4175 4250 4550 4025 4700 0 3% 3950 4100 41]) 4400 4550 In this table the amount of stearic acid used in the nine tests listed is shown at the left of the table. At the top of the table is shown the grinding time inhours. The body of the table gives the tensile strength in pounds per square inch of the cured rubber compositions containing the whitings ground for the various lengths of time specified.

In the first instance, unground whiting was used as indicated by zero grinding time, and the rubber composition had a tensile strength of 3000 pounds. In the second instance, the plain whiting without any stearic acid was ground as long as eflective grinding could be continued, or until the whiting was about to become compacted where further eil'ective grinding could not be had. As shown on the table, the eifective grinding could not be continued beyond minutes. The tensile strength imparted to the rubber by this whiting was 3500 pounds. In the examples numbered 3 to 9, various amounts of stearic acid were incorporated with the whiting when put into the grinding mill, and the whiting in each instance was ground to substantially the end of the free flowing state or until the whiting was about to pass from the free flowing state into the compacted state. As shown in the third example, the addition oi. of 1% stearic acid prolonged the eflective grinding time to Y: hour and the whiting thus ground when incorporated in the rubber gave a tensile strength of 3900 pounds. Grinding beyond the hour would have resulted in the compacting of the whiting. In the fourth instance the use of V of 1% stearic acid prolonged the free flowing period to 3 hours, and the rubber composition had a tensile strength of 4300 pounds. In the fifth instance, the addition of V of 1% of the stearic acid prolonged the free flowing period to 5 hours. In this instance, as also in Examples 6 to 9, inclusive, samples of the whiting were taken at the end of ..each hour grinding and used in making rubber compositions, and the tensile strengths imparted noted in each case upon the table.

As shown by the table, the optimum amount of stearic acid for the precipitated whiting in question was about 1% to 2%. This prolonged the free flowing period to 6 hours, and, as shown by the table, the tensile strength imparted to the rubber was increased as the grinding'was continued up to the limit of attrition made possible by the prolongation of the free flowin'g period. As shown by the 9th example, increasing the amount of stearic acid to 3% resulted in a decreaseinthegrindingtimepermitted,alsoadecrease in the tensile strength or the rubber.

In each instance, if the grinding were continued beyond the times indicated, the material the stearic acid anti-compactant.

yond that which would be had without the stearic acid. There is an optimum amount of stearic acid to be used, and also an optimum grinding time, for the particular material being treated, which, as shown in the table, is about 1 to 2% stearic acid and about 6 hours grinding time, which was substantially the limit of grinding before the material. was about to pass from the free flowing to the compacted stage. An amount of stearic acid above the optimum amount cuts down the effective grinding time and also the.

bondability of the whiting with the rubber, probably because the stearic acid in excess of the limited amount required to form the molecular films on the particles, tends to cause the mass to agglomerate, and also because excess acid not thus firmly united with the whiting particles as interbonding films probably exerts some deleterious effect upon the rubber composition.

' While, as shown by the results of the table, it is preferred to grind the whiting to substantially the -end of the free flowing period when it is about to pass from the free flowing to the compacted state, since this appears to be the optimum tial portion of the free flowing period. In each instance, however, it will be noted that the markedly increased tensile strengths were not attained until the whiting had been ground with the stearic acid for several times the fifteen minute period which was the limit of attrition without Parts by weight Rubber (smoked sheets) 93 Zinc oxide Sulphur 3. 5 Diphenylguanidine 1 Whiting 47 The same amount of whiting was added to the rubber stock on therubber mill in each case, and after the stocks were milled, they were molded and cured for 30 minutes at 293 E, which was the optimum cure for each stock. The molded test pieces were then tested fortensile strength at break in the usual way.

While we prefer to use hardened steel balls because of their weight and resistance to abraslon, other grinding elements can be used, such, for example, as porcelain balls, flint pebbles, steel slugs, or steel rods. We prefer to use a mill of the class comprising ball mills, pebble mills and rod mills. Mills of this type consist of a rotating shell containing a large number of loose tumbling grinding elements which have a large aggregate surface area and which are in intimate contact with each other during the grinding, so as to give effective attrition upon powdered materials. In using such mills we have found that for efiicient grinding the average diameter of the grinding elements, such as the balls, rods or pebbles, should be under 2 inches, and that they should occupy at least 15% of the volume-of the mill, and that the mill should be rotated at not less than about 25% of the critical speed.

In grinding in a ball mill there are four stages of ball condition. The first is the rolling stage, whereby the balls merely roll along in a shell as the cylindrical shell rotates. This is induced by low speed and low ball volume loading. The second stage is that of cascading, where the balls are lifted up to about 10 on the clock scale and cascade over one another back down to the bottom. The transition from the first to the second stage is induced by increasing the speed of rotation of the shell. Upon further increase of the speed of rotation, the cataracting speed is obtained, wherethe balls are raised just short of position 12 on the clock scale and dropped. The fourth speed is one where the critical speed is exceeded and the balls adhere to the periphery of the mill due to the excessof centrifugal over gravity force. At this speed there is no grinding. Fine materials cannot be satisfactorily ground by the rolling stage action. A cascading action is more desirable than rolling, but we have found that the cataracting action is most desirable in our process, and we therefore prefer to so regulate the speed and ball load that the cataracting' effect is obtained. Similar action is obtained in a rod mill and we prefer to operate a rod mill so as to get the cataracting effect of the rods.

We prefer to use precipitated or artificial whiting as the raw material, particularly in preparing our material for paints, for the reasons outlined above. However, other whitings can be used, such, for example, as natural chalk whiting or limestone, particularly for purposes where color and particle size are not so important.

The alkaline earth metal carbonates as a class exhibit grinding properties similar to whiting. When subjected in a powdered condition to con-' tinued grinding in a ball mill they tend to compact, but when groundwith a small amount of a suitable anti-compactant interbonding agent there is induced the prolonged free flowing state which permits the efiective grinding to be continued for a period several times that possible without such agent.

We prefer, in carrying out our process, to thoroughly dry the precipitated whiting before grinding it with the anti-compactant and interbonding agent. These agents are organic materials and if the material is ground wet and then dried there is a tendency for them to become discolored in rapid drying. There is also a tendency to foam in the mill. However, it is possible to grind a wet slurry of precipitated whiting, provided a slurry of the right consistency is employed, neither too thick nor too thin. If the slurry is too thick it cannot be ground, and if it is too thin the particles are too diffused for grinding. The water in the slurry does not have an action like that of an excess of oil in the making of paste, since the water does not act as a lubricant and interfere with the attrition effect 10 The specificanti-compactant or interbonding agent employed depends upon the use of the materlal. In preparing precipitated whiting for use in paints, we prefer to use rosin or calcium resinate, or other resinous materials, and by a resinous material we mean to include not only the resins, but materials which are convertible into resinous substances, such, for example, as the drying oils or drying oil fatty acids. A small amount of linseed oil or linseed oil fatty acids may be employed. In the prolonged grinding of our process, the linseed oil or linseed oil fatty acids are subjected to an oxidizing action which converts them into resinous oxidized products forming films on the particles, probably similar to the calcium resinate films formed by using rosin. Other resinous substances may be used,

' such as ester gum, phenol aldehyde condensation products, and other natural or synthetic resinous substances. While we prefer to use resinous sosubstances as the interbonding agents for materials to be used in paints since they are in general more compatible with paint oils, other interbonding agents may be employed which will form a firm linkage between the carbonate par- 85 ticles and the paint vehicle, such as the organic acids and salts or soaps thereof, some of the higher alcohols such as stearyl and lauryl, phenols, and in fact any other organic material which is capable of forming such bond as evi- 40 denced by actual tests when used to treat the, fillers above described according to our process and then tested in paint.

In making a filler for rubber compositions, we

prefer to use stearic acid since it is cheap and is 4 also generally recognized in the rubber trade as being a desirable material to have in rubber rather than undesirable material. Stearic acid has an activating effect on certain organic accelerators in the rubber which is desirable. It also has a greater anti-compactant efiect than most other organic acids, such, for example, as acetic acid. However, instead of stearic acid other agents may be used. Next to stearic acid we prefer touse calcium stearate, which has an effect very similar to that of stearic acid. However, the organic acids or salts or soaps of organic acids can, in general, be used, as they as a class have an anti-compactant and interbonding action. For example, propionic acid, normal butyric acid, abietic acid or rosin, 'benzoic acid, phthalic acid or phthalic anhydride, or salts or soaps of such acids, may be employed, as well as some of the higher alcohols, such as stearyl and lauryl, phenols, and in fact, any

other organic substance which is capable of forming a strong bond between the filler particles and the rubber as evidenced by actual tests when used to treat the filler above described according to our process and then tested in rubber compositions.

The general formula of an organic acid or salt or soap of such acid, may be expressed as x-(COOR) n, in which X is an organic radical audit is either hydrogen or a metal. x is preferably a hydrocarbon radical.

The effects of treating the whiting by our process are not discernibleby microscopic examination or by other simple laboratory tests, but can be best shown by the action of such treated whit-- ing when incorporated, for example, in rubber, 5 or in paints, which are the two purposes for which the material has so far been commercially developed.

The physical characteristics of precipitated whiting treated in accordance with our inven- 19 tion may be summed up as follows as to the eifects on rubber: v

1. Rapid dispersion in rubber. It disperses more rapidly than carbon black or untreated whiting, and in fact, more rapidly than any 15 .other rubber filler of comparable particle size,

such as blanc fixe and zinc oxide. Because of its fast dispersion the rubber may be milledmore rapidly and there is less brealdng down of the rubber than with less dispersable fillers. Danger go from scorching is also minimized.

2. It has a decided reinforcing eflect on the rubber, increasing its tensile strength and resistance to wear and tear. It has somewhat the effect of carbon black in this respect, so that the g5 whiting thus treated may be classed as a reinforcing pigment, as contrasted with untreated whiting which has a weakening rather than a reinforcing eifect upon rubber.

3. It can be loaded into rubber to a consider- :0 ably greater extent than untreated whiting or other fillers commonly employed and still give the same tensile strength and other physical properties.

v4. It displays no deleterious effects on the aging of the rubber. In the cure it tends to activate certain accelerators, like mercapto-benzo-thiozole. It tends to level difierences in cure due to variations in crude rubber and does this better than blanc fixe; carbon black or untreated whit- 40 ing.

5. It induces good flow or tubing properties in rubber stocks in which it is 6. It may be used with colors in rubber because it has little or no tinting value itself in the 45 rubber.

Some of these characteristics in rubber are shown by the following tests. I

In the first test six rubber compositions were made up which were identical except for the 50 fillers used. The basic rubber stock was made up as follows:

. Parts by weight Rubber (smoked sheets); 93 Zinc oxide 5 Sulphur 3.5 Diphenylguanidine 1 This rubber stock was put onto a rubber mill and in each case 20 parts by volume of the filler tions were molded, cured, and tested for tensile strength at break, abrasion loss on the Grasselli abraders, and flexing on a DeMattia machine. Results for optimum cures are shown on the following Table 2.

Table 2 Abrasion Number 533% ere be ts.

per ore per sq. n. per hour um i Untreated precipitated whiting 4080 619 38, 900 2 Same as 1 but ground with 1% stearic acid by our process 4800 530 56,700 3 Same as 1 but ground with 3% benzoic acid by our process 4980 535 74. 500 4 Untreated talc containing some CaOO; 3500 620 18 200 5 Same talc as 4 but ground with 3.5% zinc stearate by our process 4510 427 34, 400 6 Same talc m 4 but plus 3.5% zinc stearate added on rubber mill... 3650 570 20, 600

Parts by weight smoked sheets 50 Rubber pale crepe '50 Zinc oxide u 5 Sulphur 2.5 Mercapto-benzo-thiazole 1.25

This stock. was put on the rubber mill and in each case parts by weight of whiting were added to 100 parts of rubber.

In the first case precipitated whiting was prepared by grinding with 1.2% calcium stearate in accordance with our process. In the second case the same whiting was prepared by grinding in'an ordinary type disintegrator with 1.2% calcium stearate. In the third case the same whiting was prepared by incorporating in it 1.2% calcium stearate dissolved in a benzol solution added to the whiting and then evaporated.

The resultant rubber compositions were molded and vulcanized, and then tested for tensile strength and elongation in the usual way. The results for optimum cures are shown on the followingtable:

Table 3 Tensile strength lbs. per sq. inch Elongation at break at 500%- elongation Precipitated whiting ground with calcium steal-ate by our process 3060 640 Note that the largely increased tensile strength and elongation were not attained except when the calcium stearate was incorporated with the whiting in accordance with our process- The following table, No. 4, shows the reinforcing effect of precipitated whiting treated in accordance with our process as against a pure gum stock and as against the same amount of untreated whiting used in the same formula.

In each case a basic rubber stock was first made up as follows in the usual way by compounding on a rubber mill:

An anti-oxidant aldehydeamine condensation product sold under the trade name of Agerite powder 1 In the first case the test. pieces were made up from the pure gum stock only. In the second case there was added to the pure gum stock on the rubber mill 15 parts by weight of precipitated whiting which had been ground with 1% stearic acid in accordance with our process. In the third case 24 parts of such treated whiting were added to the pure gum stock on the rubber mill. In the fourth case 40 parts by weight of 'such treated whiting were added to the pure gum stock on the rubber mill. Inthe fifth case 40 parts by weight of the same whiting, untreated, were added to the pure gum stock on the rubber mill. In each case a number of test pieces were molded from eachcomposition, and cured and tested in the usual way. The results for optimum cures are shown on the following table:

Table 4 Stress in lbs per Tensile in Percent sq. inch lbs. per sq. elongation at 500% in. at break at break elongation 1 Pure gum stock... 410 3100 '7 2 Same pure gum stoc k +l5 parts treated whiting i075 3675 730 3 Same pure gum stock+24 parts treated whiting- 1470 3425 6S? 4 Same pure gum stock-H0 parts treated whiting 1510 2805 645 5 Same pure gum stock+40 parts untreated whiting 1510 2I00 800 Note that loadings-of 15 parts and 24 parts of the treated whiting gave largely increased tensiles over the pure gum stock. At 40 parts loading with the treated whiting the tensiles at break were still high and much higher than when loaded with the same amount of untreated whiting.

Whiti'ngs and the like treated in accordance with our invention have unique properties in paints, which are further evidence of the creation of a much more perfect bond between the paint vehicle and the whiting or the like by the use of our invention. Some of these characteristics are as follows:

1. Rapid dispersion-Materials treated in accordance with our process disperse much more rapidly and completely in paint vehicles than" materials not so treated. Thus, some paints may be made without being ground 'at all, having merely been subjectedto a thorough mixing, or if it is preferred to grind such paints, they may be ground at an extremely high rate of production without sacrificein quality of the paint. This is due to the increased wetability of the surfaces imparted by our process. The dispersion effect of our treated pigments is so great that it may be used in facilitating the grinding of'poorly dispersable pigments, such as carbon black, para red and chrome green.

2. Strength and elasticity of paint films-The treated material makes a so much better bond with the paint vehicles that a more cohesive film results, which, in turn, results in greater film strength, elasticity and density (lack of porosity) at equal volume loadings than is the case when untreated materials are used.

3. Loadability.The increased strength and elasticity attained from using the treated material allows of much greater loadings to obtain films of equal strength and elasticity, as compared with any other pigments or fillers.

4. Durability of paint film. The greater strength, elasticity and non-porosity of films containing this treated material results in much greater resistance to failure from exposure to the weather. For instance, the time before chalking sets in is greatly extended by the use of these treated materials, because of the better bond which they make with the vehicle which reflects itself in the vehicle being held up around the pigment particles, so that the pigment particles are not exposed, and in the lower permeability of the film which allows less infiltration of moisture with its effect on the life of the film.

This greater bondability is further reflected in the durability of interior paint films, such as flat wall paints. Flat wall paints containing the treated material will stand much more washing without failure than wall paints containing 'any other of the usual fillers or pigments.

5. Eject on film 1 appearance; smoothness, gloss, etc-Paints containing the treated material make amuch better appearing film under comparable conditions because the increased dispersion results in complete film smoothness.

Gloss is also greatly enhanced and this is particularly true where the non-volatile vehicle percentage is comparativelyv low. Here again the extra bondability of the treated material is shown to exist in that the vehicle is held up over 6. Efiect on working properties; ease ofbrushing and spreading.'-At equal pigment loadings in comparable vehicles, our treated materials make thinner paintswhich are more easily spread and brushed than untreated materials of the same type. Here, again, the choice of interbonding agent has an influence on the property desired. .11 a state of high fiow is present, then the brushing will not be as easy as is the case with a short state. Therefore, the desired balance between how, on the one hand, and brushing ease, on the other hand; may be regulated by i the choice of interbonding age t.

'7. The use of our treated materials in connection with colors in paints has several advantages-Certain colors which cannot be made to gloss by themselves when certain loadings are employed, may be made to gloss by the use of our material in'conne'ction with-them. Treated calcium carbonate, because of its low tinting strength, as well as its glossing properties, is of particular value in this respect.

8. Non-penetrating and sealing jeatures.The treated materials, in the manufacture of which the choice of interbonding agent is such as to promote a high degree of flow, such, for instance, as calcium carbonate treated with rosin, when made into paints with flow-inducing oils or varnishes, impart properties to such paints which result in preventing them from penetrating porous surfaces. over unsized plaster walls and wall paper without penetrating, with the result that they act as selfpriming paints, retaining gloss if they are gloss paints, or their full fllm strength if they are fiat paints.

The same paints may be used as so-called sealers" for the sealing of bleeding" surfaces, such as asphalt and dyed finishes. Their function is to prevent the color from the under surface seeping through the new surface and cansing discoloration.

Some of these characteristics are shown quantitatively by the following comparative tests.

Test in 4-hour enamel-A 4-hour enamel vehi- AmberoP' resin is a synthetic resin containing about phenolaldehyde resin and 80%- ester gum. In making upthis vehicle the Chinawood oil was heated to 262 C. and held for a string. It was checkedwith lead acetate and the Amberol resin added. The temperature was raised to 275 C. and cooled again by the addition of the linseed oil and manganese and cobalt linoleater On further cooling to 205 C., the thinners (turpentine and mineral spirits) were added. This is a usual type formula for 4-hour enamel vehicle or varnish.

Six enamels were made with this varnish vehicle, using in each case a weight of vehicle equal to the weight of the individual filler, as follows:

1. Ground limestone.

2. Natural chalk whiting.

3. Precipitated whiting.

4. Precipitated whiting ground by our process with 1% rosin.

5. Precipitated whiting ground with 1% rosin in an ordinary disintegrator.

6. Precipitated whiting treated with 1% rosin dissolved in mineral spirits and then dried.

The pigment to non-volatile vehicle volume ratio calculated on these weights is approximately 1 volume of pigment to 1.3 volumes volatile paint vehicle.

The fillers were incorporated in the vehicle by 'of the nonthe usual grinding method of grinding each pigconcentrations. The times required for grinding were observed and are recorded in the following Table No. 5:

Table 5 Grinding Film time per Gloss fiexi- Body 'i g gallon bility Mn. 1 Groundlimastone. 12 Poor. 3rd. 20' Fair. 2 Natural chalk 13 Fair 2nd 22' do.

whiting. 3 Precipitated whit- 20 Very 6th 40' Bad ing. poor. pen. 4 Precipitntedwhit- 10 Excel- 1st... 18' -None.

mg ground by lent. our process with 1% rosin. 5 Precipitatedwhit- 18 Poor 5th..-. 25' Pen.

lngground with 1% rosin in an ordinary I disintegtator 6 Precipitatedwhit- 15 do 4th...- 26'. Pen.

ing treated with 1% rosin dissolved n mineral spirits and then dried.

For gloss and flexibility tests the enamels were painted with equal film thicknesses onto standard panels of tin plate. These enamels were allowed to dry for four hours and when dry, were examined for gloss. They were allowed to dry for another 20 hours and then baked at C. for 2 hours. The panels were then bent over a standard mandrel to the same degree of bend in each case and were examined for cracking. The results of these tests are shown in the above Table 5 in which the enamels are rated in the order of their flexibility. The increased flexibility of the paint film containing the whiting ground by our process was quite marked over that of the next best paint film, in that a degree of binding which caused distinct cracking of the next best film, caused no cracking whatever of the paint film containing our material.

The paints were placed in a mobilometer with no weight on the plunger and their body judged by the time it took the plunger to reach the bottom of the mobilometer. These body readings in seconds of time are recorded in the table.

Each of the paints was brushed out on newspaper and observed after 15 minutes for penetration. The results of these observations are also recorded in Table 5. Penetration of the vehicle from the enamel into newspaper is very easily discernible by examining the reverse side of the paper. Penetration is also evidenced when there is loss of gloss of an enamel painted over a porous surface as against the. same enamel painted over a non-porous surface.

Note that the grinding time required for the enamel containing the whiting treated in accordance with our process was the lowest, showing its more ready dispersion in the enamel vehicle. It is also to be noted that the same enamel was the only one to give an excellent gloss, and particularly that the enamels made with the same whiting with the rosin incorporated in other manners gave a poor gloss.

gave a film of the greatest flexibility. The

enamel made with our treated material had a lower viscosity. This, together with the higher flexibility, demonstrates the greater loadability of our treated whiting. The penetration tests were quite striking, as the enamel made with our material was the only one which did not penetrate so that the penetration was visible at the back of the paper. Neither did it lose any gloss on paper as compared with the same enamel painted on the metal surface.

Exterior paint exposure testa-A number of comparative tests were made in the exposure of exterior paints. The paint vehicle employed was raw linseed oil with a small amount of bodied linseed oil and the usual amounts of driers. Eight paints were made up by incorporating in each case the same volume of the filler or pigment with the oil vehicle as follows:

4 1. Ground limestone.

2. Natural chalk whiting.

3. Precipitated whiting.

4. The same precipitated whiting ground with .1 rosin by our process.

5. Magnesium silicate.

6. Barytes.

7. Zinc oxide.

8. White lead.

color, each to the same extent, and painted out on other panels of the test fence, and the number of months before the red color had completely faded were observed and recorded in the following Table 6:

Table 6 Exterior paint exposure tests-12 months test Months Appean Months Grind before ancealter before Fading chalk- 12 crackgallon in; months ing months o dlim io 2 Poor No 2 1 man astone. crack- 2 oi i aik whltn 4 -.do...- '3 3 Precipitated 22 2 Very ..-do- 2 w 1 poor. 4 The s a me 8 12 Good... ..-do.-... 8

precig itated w ting g r o u n d with 1% rosin by ourprocess. 5 Magnesium 25 Very do.... i

silicate. poor. 6 BBIYWS 6 6 Fall (In 6 7 Zinc oxide- 30 None Checked 8 8 at 12 and months. cracked 8 Whitelead 20 8 Good... No 6 As shown on the tests, our treated whiting had a short grinding time, indicating its ready wetability with the linseed oil vehicle. It withstood chalkingbetter thananyofthepaintsexcept zinc oxide, which, however, cracked, whereas the paint made with our material showed no cracking at the end of twelve months. Also, the paint made with our material was the only one, except the white lead paint, which presented a good appearance-at the end of twelve months. It withstood fading as long as the zinc oxide paint and longer than white lead paint.

These tests show that the whiting treated in accordance with our process can be substituted for the more expensive white leads and zinc oxides in exterior paints insofar as their elect on weathering is concerned, and the paints may be given the necessary covering power by the addition of other poorer weathering pigments, such as lithopone, titanium dioxide,- or pigments containing titanium dioxide and a barium or calcium sulphate extender- The resistance to chalking shows the strong bonding of the oil with the whiting particles treated by our process. A microscopic examination of paints and enamels containing our treated whiting shows that the paint vehicles are strongly held to the surfaces of and surround the whiting particles, completely protecting them against the elements, whereas with most fillers there is so little adhesion between the paint vehicle and the filler particles that the paint vehicle after relatively short weathering no longer adheres to and covers the particles but leaves them exposed, with resultant chalking and color fading.

Loadability.-The following table, No. '1, illustrates the greater "loadability of our treated calcium carbonate over other extenders and pigments in a fiat wall paint liquid. These numerical values are obtained by bending, to the 'same degree of bend in each case, films of equal thickness after they are completely dried.- A number of paints were made up for this test containing various percentage loadings of the various pigments and fillers to be tested.

As a result of the bending tests on these paints, certain of the paints were found to cracking in an equal degree. These paints are grouped together and their compositions considered in terms of ratio of pigment volume to non-volatile vehicle volume, and the results recorded are expressed in these numerical values for films of equal degrees of flexibility:

Table 7 Loadabilityojmriousfillersmdpiamentshsflat 'wullpaintliqiud Precipitated whiting ground with 1% mm by our The commercial significance of this test lies in the fact that the more heavily loaded the film, 'all other things being equal, the greater the hiding power of that film. Therefore, when our treated calcium carbonate is used in this connection, higher pigment concentrations may be used and high hiding powers may still be obtained by the substitution of a. certain amoimt of our material for high priced lithopone'. An example is as follows:

The following two paints have exactly equal qualities as regards hiding power, film strength and elasticity, brushing ease, and washabilityz- Paint A costs 53 cents per gallon for raw materials and paint B costs 42 cents per gallon, at present prices:

Point A Percent by volume Ordinary whiting or magnesium silicate-.. 11.2

Lithopone 22.4

Volatile vehicle (mineral spirits) 45.1 Non-volatile vehicle (bodied linseed oil and drier or combination of bodied linseed oil and Cliinawood oil) 21.3

Paint B Percent by volume Whiting which has been treated with 1% rosin by our process 30.85 Lithopone 11.05 Volatile vehicle (mineral spirits) 42.9 Non-volatile vehicle (same as in A) l5.2

While we have described our invention more particularly with relation to the manufacture of our prebonded preciptated whiting and its use in paints and rubber compositions, materials made in accordance with our process may be employed for other purposes, such, for example, as in the making of other plastics including coating compositions. For example, the treatment ing good bondability with the organic binder may be desired.

It is to be understood, therefore, that the present invention is not limited to the details of the specifically described methods and embodiments, but may be otherwise embodied and prac: ticed within the scope of the following claims.

We claim:

1. The process of preparing whiting for fillers, which comprises grinding the whiting with an organic interbonding agent with such severe and prolonged attrition that the bondability of the whiting with the usual organic matrices employed in paints. rubber, and the like, is greatly increased over that obtainable by grinding the whiting without such agent and over that obtainable by incorporating such interbonding agent with the whiting without such prolonged attrition, the amount of interbonding agent used being not less than about .1% of the whiting but less than that which would form a viscous paste with the whiting in the grinding operation or leave an objectionable uncombined excess in the finished product.

2. The process of preparing alkaline earth metal carbonates for use as fillers, which comprises grinding the carbonate in a finely divided condition for a period several times that possible if .the carbonate were ground alone, the grinding being carried out with the addition to the carbonate of an anti-compactant and interbonding agent which serves thermal function of greatly prolonging the eifective grinding period and of imparting to the product increased bondability with the usual bonding matrices, the amount of anti-compactant and interbonding agent used being not less than about .1% of the carbonate but less than that which would form a viscous paste with the carbonate in the grinding operation or leave an objectionable uncombined excess in the finished product.

3. The process of preparing alkaline earth metal carbonates for fillers, which comprises grinding the carbonate in a finely divided condition with an interbonding agent with such severe and prolonged attrition that the bondability of the filler with the usual bonding matrices is greatly increased, the amount of interbonding agent used being not less than about .1% of the carbonate but less than that which would form a viscous paste with the carbonate in the grinding operation or leave an objectionable uncombined excess in the finished product.

'4. The process of making reinforcing fillers for rubber mixes, which comprises subjecting an alkaline earth metal carbonate to prolonged grinding in a mill having loose tumbling grinding elements with .1 to 5% by weight of a coinpound having the formula X-(COO-R) n, in which X is an organic radical and R is either hydrogen or a metal, the grinding elements being under 2 inches average diameter and occupying at least 15% of the volume of the mill, the mill being rotated at not less than 25% of critical speed, whereby the vulcanized rubber mix containing such filler has imparted thereto increased tensile strength, resistance to wear and resistance to fatigue, as compared to a similar mix made from the same alkaline earth metal carbonate and with the same amount of said compound, but not having been treated in accordance with the above described grinding conditions.

5. The process of making reinforcing fillers for rubber mixes, which comprises subjecting a whiting toprolonged grinding in a mill of the class composed of ball, pebble and rod mills, with .1 to 5% by weight of a compound having the formula X(COOR)n, in, which X is an organic radical and R is either hydrogen or a metal, the grinding elements being under 2 inches average diameter and occupying at least 15% of the volume of the mill, the mill being rotated at not less than 25% of critical speed, whereby the vulcanized rubber mix containing such filler has imparted thereto increased tensile strength, resistance to wear and resistance to fatigue, as compared to a similar mix made from the same whiting and with the same amount of said compound, but not having been treated in accordance with the above described grinding conditions.

6. The process of preparing fillers for paints from alkaline earth 'metal carbonates, which comprises subjecting an alkaline earth metal carbonate to prolonged grinding in a mill having loose tumbling grinding elements with .1 to 5% by weight of a resinoussubstance which serves as an interbonding agent in markedly increasing the bondability of the carbonate with the usual paint vehicle when such interbonding agent is intimately incorporated on the carbonate particles, the grinding elements beingunder 2 inches average diameter and occupying at least 15% of the volume of the mill, the mill being rotated at not less than 25% of critical speed, whereby the paints containing thereto an increased strength, elasticity and durability of the paint film, as compared to a similar pa int composition made from the same such fillers have imparted alkaline earth metal carbonate and the same amount of said resinous substance, but not having been treated in accordance with the abovedescribed grinding conditions.

7. An improved paint characterized in that it comprises an alkaline earth metal carbonate which has been subjected to severe and prolonged attrition in a mill having loose tumbling grinding elements with .l to 5% by weight of a resinous substance which serves as an interbonding agent in markedly increasing the bondability of the carbonate with the usual paint vehicles when such interbonding agent is intimately incorporated on the carbonate particles, the grinding elements being under 2 inches average diameter and occupying at least 15% of the volumeof the mill, the mill being rotated at not less than 25% critical speed. V

8. An improved paint characterized in that it comprises precipitated whiting which has been subjected to severe and prolonged attrition in a mill of the class composed of ball, pebble and rod mills, with .1 to 5% by weight of a resinous substance which serves as an interbonding agent in markedly increasing the bondability of the carbonate with the usual paint vehicles when such interbonding agent is intimately incorporated on the carbonate particles, the grinding elements being under 2 inches average diameter and occupying at least 15% of the volume of the mill, the mill being rotated at not less than 25% critical speed.

9. The process of preparing whiting for fillers, which comprises precipitating whiting in a finely divided condition, drying the precipitated-whiting, and subjecting the dry whiting to severe and prolonged attrition with from about .1 to 5% of an organic material containing an acidic radical which combines with calcium to form an organic calcium salt and which serves the dual function of an anti-compactant in causing an evolution of gas in the whiting being ground and inducing a free flowing state prolonged several timrs beyond that obtainable when the whiting is ground without such anti-compactant and of an interbonding agent in increasing the bondability of the whiting with the usual organic matrices employed in paints, rubber and the like, when such interbonding agent'is intimately incorporated on the whiting particles, and continuing the grinding during the greater part of such free flowing state, whereby the anti-compactant interbonding agent is ground into sufilciently intimate contact with whiting particles to markedly increase their bondability with the usual organic matrices over that obtainable by incorporating such interbonding agent with the whiting without such prolonged grinding, and over that ohtainable by grinding the whiting to the limit of 'attrition possible without the anti-compactant "interbonding agent.

10. The process of preparing whiting for fillers, which comprises precipitating whiting in a finely divided condition, drying the precipitated whiting, and subjecting the dried whiting in a mill of the class'composed of ball, pebble and rod mills, to prolonged attrition with an organic material which serves the dual function of an anticompactant to cause an evolution'of gas in the whiting being ground and inducing a free flowing state prolonged several times beyond that obtainable when the whiting is ground without such an anti-cqmpactant and of an interbonding agent in increasing the bondability of the whiting with the usual organic matrices when 1% of the whiting and sufllcient to act eflectively as an anti-compactant and interbonding agent but insuillclent' to interfere with the dry free flowing characteristics of the whiting.

11. The process of preparing alkaline earth 5 metal carbonates for fillers, which comprises subiecting the carbonate in a dry, ilnely divided condition to severe and prolonged attrition with about .1 to 5% of an organic material which serves the dual function of an anti-compactant in causing an evolution of gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the carbonate is ground without such an anti-compactant and of an interbonding agent in increasing the bondability of the carbonate with the usual organic matrices when such interbonding agent is intimately incorporated on the carbonate particles, and continuing the grinding during the greater part of-such free flowing state, whereby the anti-compactant interbonding agent is ground into sumciently intimate contact with the carbonate particles to markedly increase their bondability with the usual organic matrices employed in paints, rubber and the like over that obtainable by incorporating such interbonding agent with the carbonate without such prolonged grinding and over that obtainable by grinding the carbonate to the limit of attrition possible without the anti-compactant 0 interbonding agent.

12. The process of preparing alkaline earth meial carbonates for flllers, which comprises subjecting the carbonate in a dry, finely divided condition to severe and prolonged attrition with about .1 to 5% 01' a resinous material which serves the dual iunction of an anti-compactant in causing an evolution of gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the car- Y bonate is ground without such an anti-compactant and of an interbonding agent in increasing the bondability oi' the carbonate with the usual organic matrices employed in paints and the like when such interbonding agent is intimately incorporated on the carbonate particles, and continuing the grinding during thegreater part of such free flowing state, whereby the resinous anti-compactant interbonding agent is ground into sumciently intimate contact with the carbonate particles to markedly increase their bondability with said organic matrices over that obtainable by incorporating such interbonding agent with the carbonate without such prolonged grinding and over that obtainable by grinding the carbonate to the limit of attrition possible without the anti-compactant interbonding agent.

13. The process of preparing alkaline earth me'al carbonates for fillers, which comprises sub- Jecting the carbonate in a dry. finely divided condition to severe and prolonged attrition with about .1 to 5% of a compound having the formula X(COOR)n, in which x is an organic radical and R is either hydrogen or a metal, and which serves the dual function of an anti-compactant in causing an evolution of gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the carbonate is ground without such an anticompactant and of an interbonding agent in increasing-the bondability of the carbonate with the 5 usual organic matrices'when such interbonding agent is intimately incorporated on the carbonate particles, and continuing the grinding during the greater part of such free flowing state, whereby the anti-compactant interbonding agent is grolmd 10 into sufllciently intimate contact with the carbonate particles to markedly increase their bond-- abili'y with organic matrices over that obtainable by incorporating such interbonding agent with the carbonate without such prolonged grinding and 5 over that obtainable by grinding the carbonate to the limit of attrition possible without the anticompactant interbonding agent. 14. The process of preparing alkaline earth metal carbonates for flllers, which comprises subso Jecting the carbonate in a flnely divided condition with about .1 to 5% of an interbonding agent which when intimately incorporated on the carbonate particles, increases their bondability with the usual organic matrices employed in paints, as rubber and the like, to severe attrition prolonged to the point where the carbonate exhibits markedly greater bondability with organic matrices than the same carbonate treated with such agent without such prolonged attrition or the same carbon- 30 ate subjected to prolonged attrition without the use of the interbonding agent.

15. The process of preparing alkaline earth metal carbonates for fillers, which comprises grinding the carbonate in a mill of the type com- 36 prising ball, pebble and rod mills, together with a small amount of an acidic organic material capable of reacting, at least in part, with the alkaline earth metal carbonate, and which serves the dual function of an anti-compactant in causing an 40 evolution of gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the carbonate is ground without such anti-compactant and of an interbonding agent in increasing the i5 bondability of the carbonate with the usual organic matrices when such interbonding agent is intimately incorporated on the carbonate particles, and continuing the grinding during a substantial part of the free flowing state thus induced 60 so as to grind said agent onto the carbonate particles and thereby impart to them an increased bondability with organic matrices, the amount of the acidic organic material used being not less than about .1% of the carbonate but less than that 66 which would interfere with the dry free-flowing characteristics of the carbonate.

16. The process of preparing whiting for flllers. which comprises grinding the whiting with about .1 to 5% of an organic material which 60 serves as an interbonding agent in increasing the bondability of the whiting with the usual organic matrices employed in paints, rubber and the like, when such interbonding agent is intimately incorporated on the whiting particles, 65 with such severe and prolonged attrition that the bondability of the whiting with said usual organic matrices, is greatly increased over that obtainable by grinding the whiting without such agent and over that obtainable by incorporating the interbonding agent with the whiting without such prolonged attrition.

17. A filler for plastics, consisting of a modifled alkaline earth metal carbonate produced by grinding an alkaline earth metal carbonate in a ll finely divided condition for a period several times that possible if the carbonate were ground alone, the grinding being carried out with the addition to the carbonate of a small amount of an organic anti-compactant and interbonding agent which serves the dual function of greatly prolonging the eflective grinding period and of imparting to the carbonate increased bondability with the usual bonding matrices, said carbonate filler being characterized by a much more rapid dispersion in the usual bonding matrices than the same carbonate not so treated and by a much higher bondability than the same carbonate not so treated, the amount of the anti-compactant interbonding agent used being not less than about .1% of the carbonate but insuflicient to interfere with the dry free-flowing characteristics of the modified carbonate.

18. A filler for plastics, consisting of a modifled alkaline earth metal carbonate produced by subjecting an alkaline earth metal carbonate in dry finely divided condition to severe and prolonged attrition with about .1 to 5% of an organic material which serves the dual function of an anti-compactant in causing an evolution 01' gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the carbonate is ground without such an antl-compactant and of an interbonding agent in increasing the bondability of the carbonate with the usual organic matrices when such interbonding agent is intimately incorporated on the carbonate particles, and con- 'tive grinding period and tinuing the grinding during the greater part of such free flowing state, said carbonate being characterized by a. bondability with the usual organic matrices greater than that obtainable by incorporating the interbonding agent with the carbonate without such prolonged grinding and greater than that obtainable by grinding the carbonate to the limit 01' attrition possible without the anti-compactant interbonding agent.

19. A paint containing a vehicle and a modifled alkaline earth metal carbonate, the modified alkaline earth metal carbonate being produced by grinding an alkaline earth metal carbonate in a finely divided condition for a period several times that possible it the carbonate were ground alone, the grinding being carried out with the addition to the carbonate of an organic anticompactant and interbonding agent which serves the dual function 01' greatly prolonging the efl'ecof imparting to the carbonate increased bondability with the vehicle,

881d modified alkaline earth metal carbonate being characterized by a much more rapid dispersion in the vehicle and by a much higher bondability with the vehicle than the same carbonate not so treated, the amount of the anti-compactant interbonding agent used being not less than about .1% of the carbonate but insuflicient to interfere with the dry free flowing characteristics the modified carbonate.

20. A paint containing a four-hour arnish and a modified alkaline earth metal carbonate, the modified alkaline earth metal carbonate being produced by grinding an alkaline earth metal carbonate in a finely divided condition for a period several times that possible if the carbonate were ground alone, the grinding being carried-out with the addition to the carbonate oi. an organic anti-compactant and interbonding agent which serves the dual function of greatly prolonging the eiiective grinding period and of imparting to the carbonate increased bondability with the varnish, said modified alkaline earth metal carbonate being characterized by a much more rapid dispersion in thevarnish and by a much higher bondability with the varnish than the same carbonate not so treated, the amount of the anti-compactant interbonding agent used being not less than about 1% of the-carbonate but insuflicient to interfere with the dry tree flowing characteristics of the modified carbonate.-

21. A paint containing a vehicle and a modifled alkaline earth metal carbonate, the modified alkaline earth metal carbonate being produced by subjecting an alkaline earth metal carbonate in dry finely divided condition to severe and prolonged attrition with about .1 to 5% of a resinous material which serves the dual function of an anti-compactant in causing an evolution oi. gas in the carbonate being ground and inducing a free flowing state prolonged several times beyond that obtainable when the carbonateis ground without such an anti-compactant and of an interbonding agent in increasing the bondability of the carbonate with the vehicle when such resinous material is intimately incorporated on the carbonate particles, and continuing the grinding during the greater part of such .Iree' such prolonged grinding and greater than that,

obtainable by grinding the carbonate to the limit of attrition possible without the resinous material.

' JOHN W. CHURCH.

RAYMOND R. McCLURE. 

